1. Field of the Invention
The invention relates to a multi-cylinder internal combustion engine, and more particularly relates to a multi-cylinder internal combustion engine incorporating a cylinder arrangement in which a cylinder firing interval between two cylinders located in one bank of the internal combustion engine is 180° CA (Crank Angle).
2. Description of the Related Art
Published PCT application No. JP2003-515025 discloses a multi-cylinder internal combustion engine that is configured to realize an optimum and uniform air intake rate among all the cylinders formed in one bank of the engine. More specifically, this engine is a V-eight-cylinder engine whose cylinders are arranged such that a firing interval between two of the cylinders located in the same bank of the engine is 180° CA. With regard to these two cylinders, a pressure pulse that is produced in response to the exhaust valve of the later-fired cylinder being opened after fuel combustion therein can reach the first-fired cylinder which is at this time in a valve overlap region in which the intake and exhaust valves are both open. To counter this, the cams of the exhaust cam shaft are provided with different profiles.
In addition, Japanese Laid-opened Patent Application No. 10-184404 discloses an intake-exhaust control apparatus for an internal combustion engine which reduces pumping loss without reducing the fuel economy during a partial-load condition. This engine is equipped with variable valve drive mechanisms for the intake and exhaust valves, respectively, which change valve opening/closing timings and valve operation angles, and controls a valve overlap angle these mechanisms.
According to the foregoing internal combustion engine of Published PCT application No. JP2003-515025, however, producing the different profile cams requires setting a different production process for each cam, which reduces the production efficiency. Also, even if an automatic grinding machine is used to form the cams, its grinding program must be changed for each profile, which results in an increase in the production cost. Also, the use of such different profile cams creates the possibility that the cams be mounted at incorrect positions on a cam shaft during assembly of the cam shaft.